Power distribution networks and circuits are traditionally designed and operated as a multi-phase AC feeder circuit serving AC or DC single-phase, double-phase or three-phase loads. Most commonly, distribution feeders emanating from power substations include three-phase primary lines with multi-phase branches or lateral lines along the feeder backbone to serve plural multi-phase or single-phase end users and loads. The feeder line may be sectionalized by switches and line reclosers. In addition, the lateral lines that connect loads to the feeders may be fused. However, the operation of the fuses to isolate the loads is typically not controllable either remotely or locally.
While the opened or closed status of a feeder switch is controllable, the connection between a feeder conductor and a lateral line is fixed and generally not controllable. Therefore, these current mechanisms for topology control from sources to lateral lines are limited to three-phase configurations and to discrete open and close operations in multi-phase circuits.
Many loads are only connected to a subset of the phases of a feeder. For example, the source may have three-phases, often referred to as A, B, and C phases. In the case of single-phase loads, some loads may be connected to the A phase, others may be connected to the B phase, and still others may be connected to the C phase. The connections between the loads and the source phases are typically created at the time the loads are brought into service. However, because the power demanded by various loads dynamically changes, it is desirable to find a mechanism to automatically and efficiently re-balance loads among phases. Similarly, in the case of a feeder line fault on a single phase, it may be desirable to automatically and efficiently switch loads connected to the feeder on which the fault occurred to other phases. The switching of loads to other phases may be temporary while repairs are being made to the faulted lines. Once repairs are made, it is desirable to automatically and efficiently switch loads back to the repaired phase.
Mechanisms for rebalancing loads among phases in multi-phase power distribution systems have been proposed. For example, one proposed mechanism uses separate phase changeover switches for switching between each pair of phases and switches based on zero phase current detection. Another mechanism uses a summing circuit that receives the three-phase power, converts the power to a single phase, and then distributes the single-phase power among the loads. Other phase load balancing solutions use expensive combinations of power electronics and transformers to achieve load balancing between phases. Due to their expense and complexity, such solutions are unsuitable for widespread deployment at the lateral line level.
Still another problem with proposed solutions to switch between phases is the requirement to switch to an intermediate phase when transitioning between two phases. For example, some switch designs when switching between phases A and C require that the switch make a temporary connection with the B phase when transitioning from A to C. The temporary connection to the B phase may cause transients on both the A and B phases, which are undesirable.
It is also desirable to have an efficient way for prosumers to automatically and efficiently switch between phases. A prosumer is an entity, such as a residence, that sometimes produces excess power that could be supplied to the grid and at other times consumes power supplied from the grid. When the prosumer produces excess power, it is desirable to switch the prosumer to the feeder phase most in need of the excess power. When the prosumer is consuming power, it is desirable to switch the prosumer to the feeder phase most capable of supplying the needed power.
Accordingly, there is an unmet need for a cost-effective mechanism that achieves greater topology control and phase selectivity in multi-phase circuits for power distribution systems.